mat_file  = 'D:\Projects_Cai\exemplarsvm-master-2\VOCdevkit\person detection\val_set.mat';
load(mat_file);

for i=1:length(val_set)
    s = val_set{i};
    s2 = ['VOCdevkit/person detection/jpg2/' s(end-11:end)];
    val_set{i} = s2;
end

save(mat_file, 'val_set' );